Etymology isn't the same as meaning (often far from it). "Psychedelic" means "1. relating to or denoting new or altered perceptions or sensory experiences, as through the use of hallucinogenic drugs; 2. denoting any of th drugs that produce these effects; 3. *Informal* (of painting, fabric design, etc.) having the vivid colours and complex patterns popularly associated with the visual effects of psychedelic states" (Collins English Dictionary) Its use as applied to music is metaphorical and somewhat vague.

It's more of a mental state it definitely implys a sense of weirdness and unconventionality from freedom of barriers but it usually incorporates spirituality and mysticism and metaphysics also. It's rather difficult to describe with words you'll just have to get psyched up to dig the wavelength.